...about some film star

Hello.
This is a fragment from a text-book:

“Katie and her friend were sitting in the back seat talking to each other about some film star. I think it was Orlando Bloom,” recaller Mr Hampton. “I made some comment about him, I don’t remember exactly what…”

Shouldn’t it be ‘about a film star’ and ‘a comment’ rather than ‘some film star’ and ‘some comment’?

No, both are fine.

‘some film star’ is short for the full phrase, ‘some film star or other’; and similarly, ‘made some comment’ is the abbreviated form of ‘made some comment or other’.

This expression, ‘some/someone/somehow/ somewhere/ etc or other’ is used when referring to some unspecified or unknown person, thing, manner, etc. and is used to express vagueness or uncertainty.

Note the other words used: [color=red]"…about some film star. I think it was Orlando Bloom," recalled Mr Hampton. "I made some comment about him, I don’t remember exactly what…"[/b]

Thank you for the reply.

I came into the room. It was dark but I seemed to see some chair. There was also a book-case and some book on the shellf.

So, I can use ‘some’ in this sentece to express uncertainty? I mean it was dark and I’m not sure what I saw: a chair or an arm-chair, a book or a magazine.

[color=red]I seemed to see some chair:
What would be, in the full expression, the ‘other’? : ‘some chair or other’.
If you recognize that it is a chair, that is sufficient! Why would it be important to be more specific about one chair?
Similarly, "some book on the shelf." You recognize that it is a book (not a vase, not a cigar box, not a set of DVDs - why do you need to be more specific. It’s just a book on a shelf.
compare:
[color=indigo]He was talking about some fascinating book or other he was reading. I can’t remember the title…
Here, the vagueness is about the title of the book, since there are billions of titles of books.

[color=indigo]She was rambling on about some teenage heartthrob pop singer she was crazy about. Mercifully, I can’t remember his name.

The vagueness is about the name of the pop singer, since there are countless names of singers and performers.

HENCE, in your sentence:
[color=indigo]I came into the room. It was dark but I seemed to see a chair. There was also a book-case and a book on the shelf.

OR
I was exploring the millionaire’s mansion, and walked into one of the rooms. It was dark but I seemed to see some chairs. There was also a book-case and some books on the shelf, so I guessed it must be the library.

Thank you for the explanation!